From Beaulieu to Bestival, BBC4's Festivals Britannia documentary is a history of outdoor merriment

As the makers of Synth, Metal and Folk Britannia turn their cameras on the audience, the days of battling jazzers, hippy free-for-alls, or huge convoys of crusties may be over, but outdoor rock is booming

The fest of times, the worst of times? Revellers at Glastonbury rock out to the Lightning Seeds. Photograph: Alicia Canter for the Guardian

Last year, roughly one in 10 British adults attended a festival. The Performing Rights Society estimated that around 150 festivals generated some £450m for the British economy, with just 10 events accounting for half that total. Whether you fancied dressing up at Bestival, slam-dancing at Sonisphere or waving at a BBC camera at Glastonbury, there was something for everyone. The festival circuit is now a fully enshrined, middle-class version of the aristocratic Season, making this the perfect time for BBC4's Festivals Britannia film. "My suspicion is that it wouldn't have been made even 10 years ago," admits writer and director Sam Bridger. "And it's slightly different to the other films in the series [Pop, Synth, Folk and Metal Britannia] in that it's not about one genre of music. It's really a social history of Britain in the last 50 years told through music."

The first recognisably modern festivals – overnight camping, contemporary music, young people strutting about in ludicrous clothes like the world owed them a living – were the Beaulieu jazz concerts, organised by Lord Montagu of Beaulieu from 1956 and culminating in 1960s pitched battle between modern and trad jazz fans. Veteran jazzer Kenny Ball suggests that the number of young people who'd lost much of their actual childhood to the war years created a fertile atmosphere for music festivals even before the 60s kicked in.

As a result of some superb fossicking in the archives (including unseen Super 8 footage shot by free festival veteran Chris Waite) and judicious interviews with long-time fans, promoters and bands, Festival Britannia manages to neatly subvert much of the received wisdom about the supposedly golden era of festivals. While the Hyde Park free events (1968-1971) were a direct imitation of San Francisco's Golden Gate Park concerts, any altruisitic hippy idealism was extremely short-lived. The Isle Of Wight festival was roundly denounced by many fans for trying to turn a profit and was ultimately as much about drunk Mott The Hoople lookalikes ripping down fences and baiting the police as it was any "good vibes".

With the realisation that pop culture was going to outlive the 60s, carpetbagging entrepreneurs jumped on the festival bandwagon, including a youthful Jeremy Beadle, who is seen furiously bullshitting to an interviewer that his 1972 Bickershaw Festival near Wigan is ready to open its doors despite consisting of some scaffolding and a wind-blasted field. The footage from this time shows the focus swiftly shifting from the headline bands to the crowds who moved between the various events and the usual cultural hierarchy being inverted. "It quickly became apparent that the music was just a soundtrack rather than a cause." says Bridger. "Festivals are really about people, rather than rock stars."

And as the film shows, festivals have often been about these people's ambivalence towards authority. While this has usually meant a fairly safe letting off of steam (punching someone in the face while Sham 69 play If The Kids Are United; setting fire to a tent at Reading), it has sporadically spilled over into outright confrontation. The royal-baiting Windsor Great Park free festivals (1972-1974) culminated in a battle with the police, after which the event was given a new designated site and safely neutered. "It certainly felt a bit artificial [after that]," grumbles Steve Hillage of Gong.

'Festivals are incredibly fashionable now. They used to be fairly niche things where crusties went'

Photograph: Alicia Canter for the Guardian

A gradual souring of the free festival scene continued throughout the early-80s when the "peace convoys" were swelled by a large number of dropouts from cities – one older traveller describes them as "disenfranchised … social casualties". The scene began to take on a Mad Max quality, with the convoys looking less like a voyage into a rural idyll and more a terrified escape from inner cities racked by riots and unemployment. Two years of mutual antagonism between the travellers and the police reached its apex in 1985 in Wiltshire when police blocked a convoy bound for Stonehenge and violently attacked it. Crass drummer Penny Rimbaud accurately describes the tail end of the free festival scene as "a medieval nightmare". Once again, festivals weren't – as Donovan claims at the start of the film – a space cut off from wider society, but a bellwether for its trends and problems.

This footage and also that from the 1992 Castlemorton rave depict a different world to the modern festival experience. Ironically, the subsequent Criminal Justice Act (1994) – with its prohibition on "repetitive beats" – did much to usher in a new era of legitimacy and professionalism and draw a much wider circle of people into festivals by musically diversifying them. "They're incredibly fashionable now," says Bridger. "They used to be fairly niche things where crusties went." The modern festival is a corporate, child-friendly, mainstream experience, given blanket coverage by largely uncritical media partners. The common complaint from festival veterans is that this is something to be mourned.

But if the modern festival seems more to do with paying through the nose to dress up like a pantomime cow and have your photo taken with Vernon Kaye, then that's all right; a huge part of modern culture is market-driven, childish and obsessed with celebrity, so it stands to reason that our festivals might be too.

"For a lot of people they have become a bit of a corporate pastiche of what they once were," admits Bridger, "and I think there's some who feel like it once meant a bit more. But I don't think young people really care about branding and all that stuff."

It's unclear what will happen to the festival scene with the overheated economy from which it benefited rapidly starting to cool. But as Emily Eavis points out at the film's conclusion, as our lives become increasingly virtual, the old-fashioned attractions of simply communing with other people have actually increased and will likely continue to do so. "The essence of why people go there now is probably not that different to years ago," says Bridger. "Festivals are just a reflection of wider society and that's always been true. It's a very British thing, part of our cultural DNA."